Retinal degenerations represent one of the important causes of human blindness. Their prevention and eventual treatment requires understanding the cellular and molecular mechanisms responsible not only for the survival, but also for the differentiation of retinal neurons and photoreceptors. The long term goal of grant EY04859 is to investigate these biological phenomena. The life history of each mature retinal cell includes several rounds of mitotic division, the acquisition of the postmitotic state, migration to one of the developing cell layers, and differentiation into one of the retinal cell types. The cellular and molecular mechanisms that regulate these events remain largely unknown. We are planning to approach these questions by comparing the developmental potential of chick embryo retinal precursor cells in vivo and in vitro. We will use low density, dissociated cultures in which isolated precursor cells grow in the absence of contact-mediated intercellular interactions, as well as other culture techniques that promote that type of interactions. The stage at which each cell undergoes terminal mitosis will be determined by thymidine autoradiography and/or bromodeoxyuridine immunocytochemistry. Photoreceptor differentiation will be characterized using a multidisciplinary approach both at the single cell level (by immunocytochemistry and in situ hybridization with visual pigment-specific probes), and in cell culture extracts (by immunochemistry, Northern blot analysis and the polymerase chain reaction). Tbe experiments will test predictions from several hypotheses, in order to establish whether retinal precursor cells remain uncommitted (plastic) for some time after terminal mitosis, whether their differentiated potential changes as a function of the developmental stage at which they undergo terminal mitosis, whether rods and cones derived from common or from specialized precursors, and whether their differentiation is affected by retinoids and by exposure to cyclic light. Results from these studies should help us to understand not only normal photoreceptor development and function, but also the mechanisms leading to their disease and degeneration.